trackBorderWidth property
Border width of the track.
Defaults to 0.0.
Widget build(BuildContext context) {
   return Container(
       child: SfCircularChart(
           series: <RadialBarSeries<ChartData, String>>[
               RadialBarSeries<ChartData, String>(
                 trackBorderWidth: 2,
               ),
           ],
       )
   );
}
Implementation
final double trackBorderWidth;